1. Field of the Invention
The present invention relates to an apparatus for controlling an electromagnetically powered valve operating device of an internal combustion engine capable of electromagnetically operating intake and exhaust valves, and specifically to technologies for accurately controlling a time length of valve opening of an electromagnetically powered engine valve (substantially corresponding to a time length from a time when the engine valve starts to open to a time when the engine valve reaches its fully opened position), in particular in presence of high frictional resistance to sliding motion of a kinetic system (containing at least a valve stem of the engine valve) under low-temperature engine operating conditions, for example with a cold engine in cold weather.
2. Description of the Prior Art
Generally, opening and closing of an engine valve (an intake-port valve or an exhaust-port valve) of an internal combustion engine are achieved by way of a typical cam-drive mechanism through which the rotational speed of an engine crankshaft is mechanically reduced. However, in case of the use of a cam-drive mechanism, it is difficult to optimally control or manage an engine valve open timing and/or an engine valve closure timing and to provide an optimal valve lift, depending on engine operating conditions. In order to solve this, in recent years, there have been proposed and developed various electromagnetically powered valve operating devices which are capable of operating intake and exhaust valves electromagnetically by way of an electromagnetic force created by an electromagnetic actuator instead of the use of a cam-drive mechanism. Such electromagnetically powered valve operating devices have been disclosed in Japanese Patent Provisional Publication Nos. 7-335437 and 9-195736. The electromagnetically powered valve operating device as disclosed in the Japanese Patent Provisional Publication Nos. 7-335437 and 9-195736, includes a disk-shaped armature, often called a xe2x80x9cplungerxe2x80x9d, fixedly connected to the valve stem of an engine valve, a pair of electromagnets provided on opposite sides of the armature, and a pair of return springs biasing the armature toward a neutral position corresponding to a substantially middle position between the two opposing electromagnets. Opening and closing of the engine valve are achieved by attracting the armature alternately by the valve-opening side electromagnet and the valve-closing side electromagnet. An intake-valve closure timing (IVC), an intake-valve open timing (IVO), an exhaust-valve open timing (EVO), and an exhaust-valve closure timing (EVC) can be continually changed in response to command signals from an electronic control unit (ECU). When initiating powered opening of the engine valve, the ECU functions to move the armature from its end-of-displacement in the valve-closing direction (corresponding to a zero lift position) to its end-of-displacement in the valve-opening direction (corresponding to a maximum lift position), by breaking a holding current flowing through an electromagnetic coil of valve-closing side electromagnet and holding the armature at the end-of-displacement corresponding to the zero lift position and by applying an exciting current, often called a xe2x80x9ccatching currentxe2x80x9d to an electromagnetic coil of valve-opening side electromagnet. Application of holding current to the electromagnetic coil of valve-opening side electromagnet is continued during a valve open period. In contrast, when initiating powered closing of the engine valve, the ECU functions to move the armature from the end-of-displacement corresponding to the maximum lift position to the end-of-displacement corresponding to the zero lift position, by breaking the holding current flowing through the electromagnetic coil of valve-opening side electromagnet and by applying a catching current to the electromagnetic coil of valve-closing side electromagnet. Application of holding current to the electromagnetic coil of valve-closing side electromagnet is continued during a valve closing period.
However, the electromagnetically powered valve operating devices as disclosed in the Japanese Patent Provisional Publication Nos. 7-335437 and 9-195736, has the following drawback.
For instance, when attracting the armature by the electromagnet to initiate powered opening or closing of the engine valve, the armature would be attracted and moved to its end-of-displacement by application of catching current to the valve-opening side electromagnet or the valve-closing side electromagnet. In the presence of high frictional resistance to sliding motion of an engine-valve kinetic system (containing at least a valve stem) owing to a high coefficient of viscosity of engine oil at a very low-temperature engine operating condition, or owing to degraded engine oil, the sliding motion is unstable, and thus the valve open timing or valve closure timing, and the valve open period tend to fluctuate. This results in undesirable fluctuations in engine speed. The conventional electromagnetically powered valve operating device also suffers from the drawback that a current value of catching current applied to the electromagnet has to be increased in order to attain a full cycle of motion of the armature from one of the end-of-displacement corresponding to the zero lift position and the end-of-displacement corresponding to the maximum lift position to the other against such high frictional resistance to sliding motion. That is, there is a problem of increased electric power consumption.
Accordingly, it is an object of the invention to provide an apparatus for controlling an electromagnetically powered engine valve, which avoids the aforementioned disadvantages of the prior art.
It is another object of the invention to provide an apparatus for controlling an electromagnetically powered engine valve, which is capable of minimizing fluctuations in a valve open timing or closure timing of the engine valve, and fluctuations in a valve open period of the engine valve, that is, fluctuations in engine speed, even in presence of high frictional resistance to sliding motion of an engine-valve kinetic system containing at least a valve stem of the engine valve, owing to a high coefficient of viscosity of engine oil at very low-temperature engine operating conditions, or owing to degraded engine oil.
It is a further object of the invention to provide an apparatus for controlling an electromagnetically powered engine valve, which is capable of realizing an optimal valve open timing or closure timing of the engine valve, and an optimal valve open period without increasing electric power consumption.
In order to accomplish the aforementioned and other objects of the present invention, an apparatus for controlling electromagnetically powered engine valves, comprises an electromagnetic actuator driving an engine valve of an internal combustion engine electromagnetically, a valve-lift sensor detecting a valve lift of the engine valve, and a control unit which controls a controlled current value of exciting current applied to the electromagnetic actuator, based on the valve lift detected by the valve-lift sensor.
According to another aspect of the invention, an apparatus for controlling electromagnetically powered engine valves, comprises an electromagnetic actuating means for driving an engine valve of an internal combustion engine electromagnetically, a valve-lift detection means for detecting a valve lift of the engine valve, and a control means for controlling a controlled current value of exciting current applied to the electromagnetic actuating means, based on the valve lift detected by the valve-lift detection means, wherein the control means is configured to be electronically connected to the electromagnetic actuating means to operate the engine valve in a selected one of a normal operating mode enabling both powered opening and powered closing of the engine valve by energization of the electromagnetic actuating means, and a free-fly operating mode enabling a kinetic system of the engine valve to be free to fly according to a damped vibration system by deenergization of the electromagnetic actuating means.
According to a further aspect of the invention, a method of controlling an electromagnetically powered engine valve of an internal combustion engine having an electromagnetic actuator driving the engine valve electromagnetically, and a valve-lift sensor detecting a valve lift of the engine valve, the method comprising operating the engine valve in a selected one of a normal operating mode enabling both powered opening and powered closing of the engine valve by energization of the electromagnetic actuator, and a free-fly operating mode enabling a kinetic system of the engine valve to be free to fly according to a damped vibration system by deenergization of the electromagnetic actuator, calculating a damping coefficient as a ratio of a valve lift detected by the valve-lift sensor during the free-fly operating mode to a valve lift detected by the valve-lift sensor during the normal operating mode, calculating a desired valve open period from a time when the engine valve starts to open to a time when the engine valve closes, based on engine speed and engine load, and controlling a controlled current value of exciting current applied to the electromagnetic actuator based on the damping coefficient and the desired valve open period.